This study is a research and industry sponsored Phase IV safety study of Synagis. This is a monoclonal passive vaccine for respiratory syncytial virus. The purpose of this study was to evaluate the safety of Synagis in children under 2 years of age with complex congenital heart disease. The patients received five immunizations over a period of five months with monitoring of all adverse reactions and incidence of respiratory syncytial virus infection. Approximately 250 patients were enrolled in 30 centers. Twelve patients were enrolled at the Children's Hospital of Philadelphia.